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All About Strangles (Streptococcus equi)

Strangles in horses. Taking nasal swabs for PCR testing for Streptococcus equi equi infection

Strangles is caused by a bacteria called Streptococcus equi. subspecies equi. It is a common, highly contagious infection of a horse’s upper respiratory tract. Strangles can cause large abscesses to form, make swallowing difficult, restricting breathing and is both painful and distressing for the infected horse or pony. Whilst the disease often causes considerable suffering to affected horses and ponies, most will make a complete recovery. But up to 20% of infected horses are at risk of serious or life-threatening complications.

‘Bastard Strangles’ is the development of abscesses in parts of the horse’s body beyond the upper respiratory tract and is usually fatal. Also life-threatening is ‘purpura haemorrhagica’, which is a rare complication associated with the horse’s immune system as it fights strangles bacteria.

Strangles – how does it spread?

Strangles can be passed by direct contact from horse to horse, even if they only touch briefly. But equally important is indirect contact, where bacteria is picked up from stables, field shelters, paddocks, water tanks, troughs, buckets, yard equipment, transport and people’s hands, boots and clothing. Yard dogs and cats can act as fomites for the disease. Strangles is not airborne, but the bacteria can be propelled into the environment in huge quantities, landing on the ground, on fences, clothing, equipment and other horses as an infected horse coughs and snorts.

Signs of strangles

Clinical signs include:

  • Fever temperature above 38.5 degrees Celsius.
  • Being dull and depressed.
  • Nasal discharge.
  • Loss of appetite, difficulty eating or trouble extending the head due to pain from a sore throat or abscess around the head.
  • Lymph node swelling under the jaw, behind the jaw or below the ears. These can become abscesses, which produce thick pus when they burst.
  • Cough.

The incubation period from infection is up to 21 days and the first clinical sign is often a fever, frequently appearing before bacteria are shed.

Diagnosing strangles

A veterinary surgeon will examine the horse and take swabs and samples for laboratory testing and analysis. Guttural pouch endoscopy may be undertaken with a lavage taken from both guttural pouches. Nasopharyngeal swabs may also be taken from all infected horses and any who may have been in contact with them and submitted for PCR (polymerase chain reaction) tests. Occasionally bloods may be taken to test for the presence of antibodies.

Strangles carriers

Some 10% of horses who have suffered from strangles will continue to carry live bacteria for months or even years in their guttural pouches. These strangles carriers appear healthy, making them difficult to identify, but they have the potential to infect other horses. Carriers are believed to be the most common source of strangles outbreaks and until they are treated, can trigger outbreaks repeatedly. A carrier can shed strangles bacteria at any time, but the likelihood of shedding increases during periods of stress, such as travelling, moving home, being introduced to other horses or suffering injury or illness. Strangles carriers can be identified by testing (see above) and once diagnosed and treated by a vet, they can go on to live healthy, normal lives.

Treatment of strangles

All horses testing positive for strangles and those sharing the premises and who are sick are likely to require medication. Each affected animal will need individual care. Medication depends on abscess development and progression and must be considered on a case-by-case basis. Treatment includes medication to reduce the fever and pain associated with the lymph node abscessation. Anti-microbials are administered for the infection at certain stages of the disease.

Nursing care of the individual animals is essential – ensure they can eat by soaking feed to make it easier to swallow, raise the feed bowl so the horse does not have to bend its neck, and apply a hot compress to any developing abscesses and bathe burst abscesses.

Prevention and management of strangles

A separate detailed article on the prevention and management of strangles can be found here on this website.

Rely on your veterinary practice for support and guidance. Veterinary medical advice is evidence based and you can be sure your vet will provide sound professional advice, taking into account the facilities at your yard, the number of people available to help you and any other relevant factors. Do not be afraid to discuss the financial aspects of a strangles management plan, right at the outset.

Redwings, the horse sanctuary charity, has prepared an excellent resource on strangles in conjunction with Dr. Andrew Waller (formerly of the AHT), Jan Rogers (Horse Trust), Prof. Josh Slater (RVC), Roly Owers (Equine Disease Coalition, World Horse Welfare). The guide, which is endorsed by the British Horse Society and British Equine Veterinary Association, has been drawn upon in the preparation of this article.